opera glass

An opera glass is a small, low-power binocular instrument without prisms, designed for use at the opera or theater. It is a type of binocular, which is an optical instrument that provides a magnified, stereoscopic view of distant objects using two similar telescopes, one for each eye, mounted on a single frame. While most binoculars use prisms to erect the image and allow for a folded light path, opera glasses typically have simpler lens systems and narrower fields of view, with magnifications usually ranging from 2.5x to 5x. They are often used in the plural, as "opera glasses".12